The present invention relates generally to digital systems for signal reception and processing, and more particularly for reducing the effects of random additive impulse interference.
Radio communication and location systems are susceptible to various forms of noise that can disrupt signal reception. Random impulse noise, which comprises one or more pulses with relatively high amplitude and short duration, is a commonly encountered noise. Generally speaking, sources of random impulse noise include microwave ovens, washing machines, light switches, car engines, and other electrical machines. Severe impulse noise can degrade signal reception quality and cause burst errors to occur. To ensure quality signal reception, system designers often install an apparatus in the receiving path of a receiver to detect impulse noise and remove it. However, since impulse noise can have various different properties, detection of impulse noise is a complex task. In the related art, there are known methods and apparatuses designed for negating random impulse interference. For example, in U.S. Pat. No. 7,706,542 the device contains a Noise Extraction Unit, a Hold Unit, a Noise Smoothing Unit, a Hold Control Signal Generation Unit, a Low Pass Filter, a Comparator, and an Absolute Value Circuit; however, the device is intended for removing impulse noise whose duration is much less than the period of the carrier or intermediate frequency. In addition, the device cannot be directly used in radio systems with digital modulation. Further, U.S. Pat. No. 7,103,122 discloses a noise canceller which includes a Noise Detector, a Switch, a Hold Circuit, and other components. In this patent the duration of noise is assumed to be much less than the period of the carrier oscillation. Strobe and impulse noise processing units of a Synchronous Code Division Multiple Access (SCDMA) system (Chip Blanking and Processing in SCDMA to Mitigate Impulse and Burst Noise and/or Distortion), described in U.S. Pat. Nos. 7,573,959 and 7,236,545, contain a Delay Block and a Impulse Noise Detection Block; however, such units are designed to remove impulse noise with a limited duration.